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It is widely accepted that solar active regions including sunspots are formedby the emerging magnetic flux from the deep convection zone. In previousnumerical simulations, we found that the horizontal divergent flow (HDF) occursbefore the flux emergence at the photospheric height. This Paper reports theHDF detection prior to the flux emergence of NOAA AR 11081, which is locatedaway from the disk center. We use SDO/HMI data to study the temporal changes ofthe Doppler and magnetic patterns from those of the reference quiet Sun. As aresult, the HDF appearance is found to come before the flux emergence by about100 minutes. Also, the horizontal speed of the HDF during this time gap isestimated to be 0.6 to 1.5 km s^-1, up to 2.3 km s^-1. The HDF is caused by theplasma escaping horizontally from the rising magnetic flux. And the intervalbetween the HDF and the flux emergence may reflect the latency during which themagnetic flux beneath the solar surface is waiting for the instability onset tothe further emergence. Moreover, SMART Halpha images show that thechromospheric plages appear about 14 min later, located co-spatial with thephotospheric pores. This indicates that the plages are caused by plasma flowingdown along the magnetic fields that connect the pores at their footpoints. Oneimportance of observing the HDF may be the possibility to predict the sunspotappearances that occur in several hours.

Detection of the Horizontal Divergent Flow prior to the Solar Flux Emergence